Profitability of invention vs skill farming?

I have a bunch of extra research skills I trained wrongly thinking I needed a bunch for research agents. I could extract them as the beginning of a skill farm since I'm not really using those sp and I've run out of things I really need to train at around 70m sp. OR I could use them to do invention and keep the skills.

Which is more worthwhile? Keep in mind I'm actively playing on the char so getting a head full of billion is implants for skill farming is probably beyond me. So is any invention that requires more than about 5bn startup costs.

I'm leaning towards skill farm simply because it won't tie me to any location or schedule, while running a t2 production chain might be profitable it's also a big spreadsheet lift plus new PI installations plus manufacturing stuff like blueprints...complex.

Which one is better to do with these sp?