The STI Trojan would not be competitive at the master/grand master grade levels, the Double stack magazines are simply easier to load. Here in OZ we are restricted to ten round magazines as well. I haven't seen anyone shooting at the upper levels with a single stack. There are a bunch of single stacks in the lower grades.
The Bul M5 IPSC model is competitive against the STI 2011 frames, Our national grading officer regularly places in the top three in Standard Division using one. I would hesitate to buy a base model Bul, it really needs the magwell, adjustable sights & ambi safety for IPSC work.
If you get a Trojan, buy a Smith & Alexander magwell. This will help with your reloads.
In summary, the Trojan is a good quality firearm, you can have fun with it, but if you want to move up the grades, buy something else.