The best avalible option for acceleration and highway driving would be an LS transmission with a modified final drive. By scaling it to the same top gear ratio as the GSR you're left with something that hits 35mph at 8k rpm in first and 160 at 8k in 5th. Though I find it utterly pointless, just stick with a GSR transmission.

The major gains for the a VTEC conversion utilizing an LS crank come from the extra compression, not the displacement. Though the extra displacement does net higher gains, the "miracle" worker is just the taller stroke pushing the pistons closer to deck height.