Here is a list of the basic specs.
I also had a BX25D and considered the B2601 but saw it as not a big enough weight or hydraulic performance jump to be worth the money. So I decided I was moving to the next chassis size up, or just going to stay where I was with the BX. I moved up and I am really glad I did. While my BX was great and all that.... it was FRUSTRATING to me because it just always ran out of hydraulic power trying to dig or lift. With the B2650, I saw a significant and very appreciated increase in every measurable performance indicator on the machine.
Loader is +27% on the B2601 and +54% on the B2650.
3 Point lift @ 24" is +113% on the 2601 and +154% on the 2650.
Your only talking about a 3" height spread between the 3, the 2601 being the shortest height.
But, you mention space restrictions. My garage opening fits the 2650 with about 2" to spare, so I was good on that. The cost for you to take a $12,000 trade on that BX25B TLB and spend a total invoiced cost of about $25,000 on the 2601 leaves a cash hole of $13,000 pre-tax/KTAC. Add in sales tax and KTAC and your up another $2,500 or $3,000... so loan value of around $16,000. That is a $16,000 jump that I could not stomach personally, I went another $1,500 up to the 2650 version TLB and felt that I was buying more everything and getting more return on my dollars. I do not regret it one bit!
EDIT:
Oh, a B2650 TLB can be tucked to 14'-7", with the backhoe turned 90°. But I just left my backhoe outside and covered it with a quality tarp.