im in the same boat you are, and i just ordered an mt-4 last night.

the reality hit me when i dropped some tenths using my friends dx2s over my 3pks. my laps were more consistant and i actually used my brakes accurately for the first time ever.

pretty sure my 3pks was a higher end radio but the spectrum was more comfortable.
i might miss the dropdown, but all i ever used on my 3pk was expo and fs. to further salt the wound, i did the same laps with his xp3-ss system. so really. all the features and speed are nice, it takes one more element out of the mix, but in the end, all about the driver.
buy the radio you LIKE best.
now i can spend the extra $300 on replacing 4 receivers. and hey, once you get into an mt-4, your not starting from scratch if you DO want an m12.