Yeah, it's a long one alright, put I'd reckon if things are planned out just right, and with a lot of save scumming, It'd be doable in 150 ish, maybe 200 hours at most, I'm just about to finish my third run on tactician, so I know the game in an out, up and down. Tactician only really got a hard wall going in this last stretch and final area (apart from a few odd encounters), maybe ten hours left and doing murder spree's of everyone I've completed quests with just to get EXP.  I'd reckon if I plan Honour mode out just right, kill everything down to the rats and wildlife for EXP, I could get the plat within the 500 hour mark, I'm at about 300 now on three separate saves However, no shame in doing Explorer mode your first time through, it won't impact the story but if you have the patience I'd recommend Classic, just as it brings out a few more of the finer details of the combat system, most everything can still be gotten through without hassle with some thought or side tracking and you won't be able to over level as much which is a problem in the second half of the game on explorer which gets boorishly easy. If you are doing a Co-op run, which is HIGHLY recommended, go for at least classic if not tactician, you'll never want it to end ^^

By any chance have you tried Wasteland 2?