Gista Mono Black Solar Panels

Spoons205

I've paid a deposit for a 12 panel solar system, but am being offered an upgrade on the panels. I have no idea how to calculate which offer gives me the best return. The installers are saying both system will pay for themselves within 6 years,

£6500 for 12x 260w Gista Mono Black 3.12 kw total
£8950 for 12x 330w BenQ Sunforte Mono Black 3.96 kw total

I have now checked the original quote and I can find very little information about the Gista Mono Black panels - does anyone know if they are any good?

6 panels on existing pitched roof
6 panels on A frames on the flat roof
Solar Edge Inverter (20 year warranty)
Solar Edge Otimizers (25 year warranty)
Schletter mounting system

Thanks