M5=awesome, but I've done some research having considered one myself and I think you'd find either E34 or E39 will be high maintenance and need a lot of attention to keep in tune.
As Terry said we've had plenty of bimmers in the past and they've been a mixed bag. All of them were six cylinders and that would be the only way to go. I've had two 325s and a 328ci before and all 3 have been good fun.
An E39 525 or 530 sport would make a great cruiser but they're auto only. Being a 5, depreciation means you could get yourself a lot of car for your money though. I know many criticise the reliability of bmws, but the E39s really were well screwed together. The cooling system *is* an Achilles heel however.
3 series would probably mean E46, still a great shape and longer scheduled servicing intervals than both te previous E36 and E39. As someone said, rear subframe cracks were a common problem. Being used to the power of your GTR I think you'd find a 323i or Lexus IS200 quite slow... A 325, 328, or 330 will offer good poke, about 7.5, 7.3, or 7.0 sec flat to 100kmh respectively for the steptronic sedans. See if you can score an '01 330ci coupe or 330i sedan which will have xenons, sunroof, leather sport seats, 17s, leccy seats with settings memorised in the key, cruise, and other nice stuff. If you can get one with sat nav that'd be a bonus as they changed from being std fit in 328ci to an option for 330ci. 8 airbags are standard for the e46.
For reference, the W210 E class of similar era were renowned for breakdowns while the equivalent BMW E39 has proved significantly more reliable. Around this time, mercedes were undergoing significant expansion in production and introducing new models, subsequently letting their quality standards slip. They've recently worked hard to turn this around
As another option a v35 would be like a budget version of a BMW coupe; you could also go an R32 Golf?