I would stay at 5x5 and see how things go.When I started the TM I started on volume day with 5x3 and things were slow moving, I changed to 5x5 and things got moving faster.Volume really is quite important on this day I think and recovery can be enhanced by altering wednesdays (your light day) workload rather than screwing with Monday needlessly.You will probably know when its time to back off on monday but for now Id get the 5x5 in and see where this takes you.

BTW Eric warned me 5x3 would not be optimal to use on Monday too.