A 1.36% error combined with a nominal 0% error from the other end should present you with few problems.
If the other end was potentially 1.36% off in the opposite direction, You're looking at a combined potential error > 2%, which would make me nervous.
A 5% error would almost guarantee problems. Consider that about 10 bits are sent to transmit a single byte. Even though everything is re-synched at the beginning of each byte, the error within a byte accumulates so that the error at the end of the byte might be 50% or more of a bit width. Depending how the UART does its bit sampling, you could end up with an erroneous value for the last bit as much as
50% of the time.Regards,
-=Dave