If this is for your initial ME CIR training and you have little or no twin time I would recommend you do it in a light training twin like a Duchess or DA42 etc. Whatever the local schools you are thinking of going with have available.
It will be far cheaper than doing it in one of these 6 seat twins you mention.
A cruise speed of 140-150KTAS is fine for training. A lot of your time will be spent flying approaches so being able to go 20-30 Kts faster is of no real value.
If you specifically want to do it in a bigger type like a Baron or C310 for some particular reason then both would be very similar in performance and costs.
Shop around and ask lots of Q before choosing a school. Quality and price will vary greatly so do your homework.
Best of luck.
