The Tiburon does 0-60 in 7-8 seconds depending on the driver, while the the WRX is a 6-7 second car. The HP to weight ratio of the cars is very similar, but I would take the H-4 turbo over the V6 NA any day. Ultimately this is a driver's race but your WRX should have the edge.
Those mods you have listed shouldn't have increased your HP as much as you think. Yes, certain synthetic fluids can increase your numbers, but I've only seen significant gains from the really expensive ones like Royal Purple, not from the everyday stuff like Mobil1 or Castrol Syntec. Your air filter isn't giving you any power since the stock airbox/filter already provide more air than the engine can use.
Your lack of an uppipe cat might help a little. The lack of a muffler won't do much if anything. The restriction in your exhaust is in the downpipe, not the muffler. And to get any gains out of changing your exhaust, you need to change your ECU programming. Just removing the exhaust backpressure won't help unless your computer is programmed to account for it. In fact, it might cause you to lose power and also give you lots of pretty lights on your dash (i.e. CELs). So do yourself a favor (and everybody else driving around you! ) and put your muffler back on. It might save you from a ticket too. So based on your mods, I doubt you've gained any noticeable amount of HP, maybe just 1-2 if you're lucky.