I bought an '87 back in '88, I've had a 2000 & still have a 2001. IMO, the 4 speed has a better gear spread. The 5 speeds actually have a slightly lower high gear. The extra gear was more of a sales tool than an improvement.

From my SSM, purchased 12/95.
87-88:
Primary reduction ratio - 1.888 (68/36)
Final reduction ratio- 2.956 (68/23)
1st. - 2.214 (31/34)
2nd.- 1.500 (27/18)
3rd.- 1.095 (23/21)
4th.- 0.875 (21/24)
95-? Don't think it's changed but that's as far as my manual goes.
Primary reduction gear -1.810 (67/37)
Final reduction ratio- 2.956 (68/23)
1st. - 2.333 (35/15)
2nd.- 1.578 (30/19)
3rd- 1.142 (24/21)
4th.- 0.956 (22/23)
5th.- 0.884 (23/26)
I just don't think it's worth it...the motor has enough torque it doesn't need it. With better jetting & a higher final ratio, in stock form the old Savages were faster on top end.