As your rank values fall in the range 1 to 50, and you want to
transform this range to -5 to +5 (a range of 10), you need to divide
your rank values by 5 and then subtract 5 from the result. Consequently
the cells that have your rank formula in at the moment can be changed
to:

=(your_rank_formula)/5 -5

You won't get a rank of 4.99, as the increments will be in steps of
0.2. The lowest rank will be -4.8.

Hope this helps.

Pete