The tape mod will not increase CPU power consumption. The tape mod reprograms the CPU pins that select the FSB. That has no effect on the pins that program the power regulator on the motherboard.
Based on actual measurements Q6600 in a GA-EP35-DS3P motherboard:
stock speed, VID = 1.2625 volts, the motherboard power regulator pulled 8.0 amps from the CPU power plug.
3.6 GHz, CPU voltage = 1.425 volts, power regulator pulled 9.5 amps.
Both values under Prime95 load.
A GTS250 will typically pull 9 amps peaking to 12 amps. So worst case CPU/GPU load will be around 22 amps. Although your PSU will not have much power in reserve, it is adequate for an overclocked CPU, stock clocked GPU, and an extra harddrive.