What's the best you can get from an iScan to JVC RPTV

I have a JVC HD-P61RU 1080p D-Ila. This model doesn't accept 1080p signals. I have been toying with the idea of an iScan VP20 or VP30 for a while. Since I am forced to pass a 1080i signal to the TV, is there any other benefis or improvements from the processor (maybe frame rate)? My sources are Dish ViP622 and Toshiba HD-A2. I mostly watch HD channels because SD looks unwatchable to me.