SM 4.0 limitation has nothing to do with preview purposes.
In our software, latest-architecture GPU is required for data processing. Modern DirectX-compatible GPU are light years ahead of CPUs in processing power. Older GPUs simply lack the floating point precision and architectural features needed for markerless MoCap algorithms.
By the way, decent SM 4.0 video cards are not that expensive. You can get a GeForce 9800 GT for as low as $95 (
http://www.newegg.com/Product/Product.a ... 6814187030). This 2-year-old video card packs many times more processing power then latest $1000 Intel CPU.