Best bright red permanent hair dye from Sally's?

High lift reds contain a lot of ammonia, (which is how they get so much lift) so are more damaging than regular permanent dyes. This is why the must only be used on virgin hair.
The best way to get bright red is to lighten to an orange shade (either with bleach or a permanent dye) and then use a really good direct dye over the top.
This will be the least damaging and also the longest lasting route to bright red hair.

Do you think I could remove some of my old red with a colour remover to lighten up to an orange and use hi lift on roots (virgin hair) and maybe match with semi dye for the rest or am I destined for patchy hair if I do that?

That sounds like it could work. I prefer a weak bleach to hi-lift dyes for roots though, you have more control and it is less damaging

Do you think I could remove some of my old red with a colour remover to lighten up to an orange and use hi lift on roots (virgin hair) and maybe match with semi dye for the rest or am I destined for patchy hair if I do that?

The best, brightest and longest lasting red I ever had was when I removed permanent red with colour b4 then bleach bathed my roots and used Special Effects (my favourite was Nuclear Red but I tried a few mixes of different ones and they were all great) the condition felt better too as I only ever had to bleach bath the roots and then top up the SFX all over to get it back to it's bright shade, I easily used to get 6 weeks out of it without touching it up!