I tried the TDI (which is actually the SSP's bigger brother) side by side in the goldfields here in Vic in a number of places against the 3500 and a 4500. The TDI with a mono coil, the 3500 with DD, we'll leave the 45 out. Was chalk and cheese. The 3500 was quieter everywhere and beat the Whites by a good 4 inches on a 59 gram nugget. Nowhere did the Whites outdo it. In high mineralisation at St Arnaud the 35 cruised, the Whites couldn't handle it until the gain was dropped down so low that depths between the two were poles apart. So the 35 won hands down with a DD coil.
If someone had a low budget and all they could afford was the Whites then yeah, why not, its Pi and gonna be better than any VLF out there and it does work ill admit. I even found some gold with it. Ill say it, its not a crap machine at all so im not in effect bagging it. If a person asked me "iv only got $1500 budget, what can I get that works in bad ground?" Id say a Whites PI.
But if someone is asking which is better between them, like the person who posted the original question, Trent, then the honest answer is the 3500.
Yeah, ok, the EMI issue. Lets face it, you go out in the goldfields, 99% of places wont have any issues with power lines or the like. Only the places near roadsides.
You can go into cancel with a 35 if there is need to. Atmospherics, you tune them out. If someone got a machine solely for the EMI issue they would soon run out of places where there was any advantage.