Variables were pretty safe at around the 900 mark pre-6.32 (the hard limit was around ~950, 50 chars for the var name should have sufficed). The pre-6.32 limit was not as consistent, though, as not all commands had the same hard limit-- I think that was mostly fixed with the new length limit.
The current hard limit is roughly 4k, or 4096 bytes, meaning you will be safe with 4000.
