If sheer speed is what you are looking for the turbo is the cheapest route. L67 cars are great at low- mid speeds. If short races are your thing then supercharging will be cheaper. L67s fall on their faces at high speeds. The only way to fix that is by getting a cam/ intercooler and running a small pulley. Keep in mind your reliability goes down with a cam. However, if your looking to run with or take LSx motors at speeds >70mph you need a turbo. Thats the only way you will continue to build speed the faster you go.
I guess this all depends on your goals and what fish you are going for.
1997 Olds LSS Supercharged. 262hp and 340ftlbs. 1/4- 15.1@ 92.04mph (stock), 2.38 60ft. Nope, I can't drive. 125,000 miles. White. Interior equipment; dual 8 way Aurora leather power seats w/ lumbar, two tone interior, theater dimming lights, CD and Cassette w/ Concert Sound III (nice), steering wheel controls, sun/ moonroof, ect. Mods: 3.5", high flow cat, 1:9s, and gutted air box w/K&N filter.
2006 Ski Doo 500SS MXZ. The 500 with the 600 motor