I'm not sure the Saurmorian Railgun is even necessary, unless you absolutely, positively need The Biggest Numbers. I'm actually kind of surprised it held on to it's Best in Slot status for Ranged Mercenaries this long. Meanwhile, the Best Melee Weapon is probably the Custom Shock Gear, not the Saurmorian Hammer. It doesn't do as much damage, but Bonus Hit Rate + Stun Chance is extremely useful (Saurmorian Hammer has an Accuracy Penalty). As far as I'm concerned, Flags are more important than raw damage. Ranged weapons are somewhat lacking in that, unfortunately. Maybe the devs are afraid of adding interesting Ranged weapons because of Rapid Fire + Second Shot.
Melee, the best loadout is probably FZR Fire Suppression System + 'Crushing' weapon. Inflict Deep Freeze with the FZR. Deep Freeze inflicts a 50 point Evasion Penalty. Each point of Evasion below 0 is 4% more damage, which is doubled by the Auto Critical with a Crushing weapon (I think). The only downside is you have a lower chance (20%) of inflicting Deep Freeze on targets that resist Freezing (instead of 50%).
For the Ultimate Character, you probably want as many perks as possible.
Myr Venom (While it's not that good an attack, it's unique and does have some exclusive content)
Pheromone Perks all stack (Musky Pheromones, Alpha Scent, Jungle Queen Scent, Pheromone Cloud)
Energizing Libido (While the description says you can gain Energy from orgasms, the real draw is it prevents you from losing Energy from orgasm, Amazonian Endurance is unnecessary. Now that higher Libido makes Teasing more effective, this is a no-brainer. Unless you took Ice Cold at character creation.)
If you're not opposed to lactation, you can restore your own Energy out of combat via Hand Milk, if you have milk in a certain range. If you have too much, you don't benefit. Also:
Mega Milk (Can always Milk Squirt, always have enough to bribe the Rat's Raiders.)
I believe it's possible to get 190 Maximum Lust, although you have at least 20 Minimum Lust and Easy (20% more Lust from Combat sources), so 170 effective Maximum Lust. (157 if you have Treated Readiness)
+15: Dr. Badger's Dollmaker. IQ B-GONE, Big Dose. (Only if you don't already have Inhuman Desire, so has to be done first.)
+15: Mitzi's Cuntnosis. (Sets to 30 if below, does nothing if you're at or above 30. Also gives Easy.)
+40: The Treatment, Any (Best to not take Amazon because)
+20: VR Adventure while Rescuing Kiro, have sex with the Salamander Hylie. (This gives you Amazonian Needs. 'Upgrades' the Minimum Lust to 40 if you already have it.)
Amazonian Needs does not stack with Treated Readiness, so with both your Minimum Lust is still 33, not 53. If you don't have Minimum Lust at or above 20, don't bother with the last step because it's not a net gain.
If you're min-maxing the Treatment (and aren't a Mercenary), you probably want to go for Cum-Cow. Dumb4Cum is extremely useful for Smugglers and overpowered for Tech Specialists (who don't need the help). +2 Maximum Intelligence/level. If you go for long enough without drinking Cum, you can actually 'restore' your Intelligence to above what it was before, if it wasn't already maxed out, so you don't have to worry about training or putting points in Intelligence. The Ditz Speech it grants is temporary and conditional, so you don't lock yourself out of Bianca, if that's something you care about.
I have a whole rant about it, but I'll spare you.
Certain types of Wings let you hit Flying enemies with Melee attacks, reach certain places faster and while expending less Energy (Zil Village, Myrellion's Deep Cave, Cave on the Eastern Edge of Uveto) and evade the Shock Hopper's otherwise unavoidable attack, while leaving your Accessory slot free for something other than the Light Jetpack.
I hear Akane's Painslut is still hilariously overpowered, if you don't mind what you have to do to get it.