you listed 2 good calibers but there are alot of factors not metioned that imo affect the choice.
1.) do you hand load?
2.) is deer the only game you will be using for this potential rifle buy
3.) how much your wanting to spend
4.) conditions where you hunt
5.) how well you shoot a mag, i say this because i prefer not to shoot mags especially without breaks. so ive found calibers that can get out there with my handloads and if i do my part. i.e. 22-6mm ack imp 1-8" twist (i hunt in tx so we can use 224 for anything)
both are fantastic rounds i have both. i have a cdl sf in 300 wsm
that shoots awesome. and i have 3 custom 6.5x284's (1 is built for hunting the rest are for the bench). one thing about the 6.5 is the sd (sectional density) and bc they are hard to beat you'd have to get a 30 cal in the 220 gr which most factory rifles are twisted to shoot to get the same from lets say a 140 gr vld in the 6.5.
may i suggest the 280 rem ack imp. 7mm are neck and neck with 6.5's look at best of the west the cal of choice is 7 mag. by the way a 7 mag you cant go wrong with. the 280 ack is one to be hard pressed to beat for accuracy and distance if loaded for and built by a good smith. just my 2 cents.