LX is exactly the same size as the old "large frame B" - the B2650. It's an almost identical machine, the only differences are minor "comfort" things (i.e. nothing in the mechanicals or frame). It is bigger than the "small frame B" - the B2601.I don't know exact specifics but the LX2610 is a bit larger and If I recall a bit more lift capacity for loader. I went LX over the B because I ended up saving money on the SU model (Was hoping for a discount on the B if they are going away but theres too much demand). I have no need for midmount PTO and welcomed the larger tire sizes as most of my property is rutted by hogs.
If you're not really worried about resale, then if you can get a good price on the B2650 buy it instead, the machine is almost identical and the money saved is money in the bank (or for implements). If you may be selling in the nearish future (near enough that you care about resale) I'd guess the LX will hold it's value better due to being the "new model". Even then, I'm not convinced that my imagined better resale on the LX would be as much as whatever saving you might have got on the B2650 - if you saved $3K now, I doubt the LX would be worth $3K more in 10 years time at the same hours and condition.