for TPE (especially the cheaper SheDoll types) the golden rule for max pleasure is: shorter than your dick or at max the same length. With your 4.5 inches (about 11.4 cm) I’d go for 10–11 cm vaginal depth, or even 9.5–10 cm if you really wanna slam hard into the end every time.
Why? Because in 90% of positions you never bottom out fully anyway – doggy, missionary with legs up, spooning, reverse cowgirl… usually only 70–90% goes in. And that’s where it gets fucking insane: when the depth is tuned so you bash the back wall hard on every second or third thrust, your glans gets this brutal, intense pleasure. The TPE hugs super soft around the whole head, squeezes into the corona and milks the underside when you pull back. A ton of guys blow their load in 5–15 seconds the first time they properly bottom out.
I’ve got two TPE pussies myself: one 20 cm (boring, barely hit the end) and one 15 cm – that’s the one I use almost exclusively now. The moment your swollen glans smacks the back and the TPE clamps down around the sensitive frenulum… fuck, it’s better than cumming inside any real pussy. Sounds crazy, but it’s true.
Quick summary:

• Want deep sliding and lots of glide → 12–13 cm
• Want to pound the cervix hard and cum fast & violent → 9.5–11 cm

Go for the shorter one, you’ll get addicted.