PLEASE READ ALL DO NOT TAKE OUT OF CONTEXT
A single 2.00" pipe will support 200+hp. 2.25" will support 300+hp. Dual systems double that. Understand that the above are ranges and in fact some have engines making more than the above. The pipe itself is rarely the restriction. As you add transitions and bends and mufflers and catalysts the effective flow SIZE of the system drops.
Twin 2.00" on a stock 1990-1994 1UZFE engine is fine as long as the other variables are done correctly. Using mandrel bends and high flow mufflers (magnaflow, borla, other straight through perforated core mufflers) should be easiest, least expensive and quietest.
Twin 2.25" if you intend to modify your engine past 300hp may be a better choice but requires careful transition design to avoid loss of low RPM response efficiency and torque.
Exhaust is both an art and a science. That is why I recommend copying the stock layout with better mufflers and Y pipes