I'd say it would hold it back, yes. But I'm not really sure how fast that processor is in todays standards.

It's pretty mediocre- comes in the high-mid range here rather than the actual high end.

I'd probably be best holding off a while in any case as the 5850 has a significant premium at the minute as it's so in demand and there's no competition from nVidia as yet.

But it would be kind of dumb not to get a gpu that supports directx 11, because within the near future many pc games will be using directx 11. And if you dont get a gpu that supports it then you wont get to play with the full experience, plus you can buy a 5750 and a 5770 for pretty cheap. 

I'm looking at building my own system and think this one suits my needs pretty well. There are some parts I would need to switch out though (due to unavailability). This is what I'm looking at:

CPU: AMD Athlon II X3 435 (I notice it isn't the same as you had, but I can't find any Irish websites that have the 440. Will the 435 be up to the task, or will I need to upgrade instead?
MOBO: ASUS M4A77TD PRO, Socket-AM3 (Again, not the exact same, but it's the closest that I could find. Will it work?)
GPU: MSI Radeon HD 5770 1GB GDDR5 (The 4890 doesn't seem to be available anywhere and I'll be playing on a 1080p monitor, so is this good?)
RAM: Corsair Dominator DDR3 1600MHz 4GB CL9 (No sign of G.Skill, but I've been told Corsair is a very good brand, if somewhat more expensive)
PSU: Corsair VX 450W PSU (Will 450W still be ok with the 5770?)
HDD: Samsung SpinPoint F3 1TB SATA2 (I think I might need the extra space)
DVD: Sony NEC Optiarc DVD±RW burner AD-7240S (Can't find Lite-On anywhere here and this seems pretty cheap)
CASE: Cooler Master Sileo 500 Midi Tower (No sign of the Centurion 5, just can't seem to get it anywhere heer, so I went with another Cooler Master that is around the same price and is presumably good enough)
Monitor: LG 22" LCD W2261VP-PF

Now that I look a it, it seems that nothing is actually the same. I tried to stay with the same template, but it's pretty hard when I have a more limited selection here. Does that look pretty similar to what you have? And, more importantly, will it be as effective and is everything compatible?

Thanks for the help,
GreyianStorm 

The difference between the Athlon II 435 and 440 is just a 100 MHz clockspeed bump, so it isn't really much of a difference at all.

Everything you've chosen looks fine, however. Can't really comment on the pricing, though, I don't know how much things cost overseas.

@GreyianStorm

Actually, the 5770 uses less power than the 4890, so the PSU will be more than enough.

Oh, well that's certainly good then :D

How does the rest of it look? I added the monitor, just so I'd have a log of everything I'm looking at. What sort of performance can I expect on games like Left 4 Dead 2, Far Cry 2, Battlefield: Bad Company 2 with this system (if you happen to know)? I'll be playing on the 1920*1080 monitor, hopefully on high-highest settings. Obviously I expect to have to compromise on the likes of Crysis, but Crysis is certainly not the average game.

Edit: Also, I've noticed there seem to be a few different 5770s: MSI, Sapphire, XFX. What exactly is the difference, and is the MSI good enough? I'm a complete beginner at this, so all help is appreciated :D

Just about anything can max out L4D2. Far Cry 2/BFBC2, dunno, however.

The difference between the brands will be the warranty, and sometimes the cooler on it. If you can, get the Sapphire Vapor-X one.

You could definitely expect to be running just about all games except GTA IV and Crysis on highest settings and still get framerates over 30 in just about every concievable situation. At least that's what I get. You'd have to skip the antialiasing though.

I have a very similar system, and I could run crysis at very high settings, but I only got 20fps, and it was not a good experience at that framerate. Everything else though (including BF:BC2) runs smoothly.

What do you consider "the near future"? At the moment, there's only a couple of DX11 games worth playing (Stalker CoP, Battlefield BC2, and Dirt 2) and all three of those run just fine on a DX10 card. And check out the ones that are announced: it's just Crysis 2, Metro 2033, and a handful of MMOs.

It's the same situation as when DX10 came out: People rushed out to become early adopters, and then games continued to be developed primarily for DX9 for years. It's only in the past year that we've finally seen a handful of DX10-only games. Don't be a sucker and fall for the same tricks again.

@ GreyianStorm: The recommended builds in the OP have already become outdated, sadly. I'll have to get around to updating them soon. In the meantime, I'll ask a mod for a sticky.