Took a counteroffer and now want to resign

You have all the right to resign. As the comment above me says - Fuck em they’ve been underpaying your for 5 years. If you hadn’t said anything they wouldn’t have bumped you up either.

Sounds like a toxic environment

Take the T1 if there’s an offer. At the end of the day, they’ve underpaid you no matter how close you are with your boss. why didn’t they increase your pay to retain you earlier if they value you? Everyone knows what the street pay is even if you’re at a T3 (especially when knowing that they’re T3 they have more of a reason to retain a strong candidate by matching the pay cuz others will bid for you).

Plus exit opps are better coming out of a T1 down the road

No matter where you are, at a place you've stayed years at and built relationships, its going to be hard to quit no matter what. You'll feel guilty, and starting to question it is normal. We all feel this way at a place you leave because of situational circumstances. Try to leave on a good note, but remember  it's your career you need to focus on at the end of the day, and what you think is best for you

Forget about your future to be ex-employer. Remind me how long you were underpaid 60%? Did they compensate for that as time too? It is their job to make sure you are paid that you do not even think of interviewing around the street.

Understandable feelings given the history - but yes, absolutely do what is best for you and your career. Loyalty is rarely rewarded and you can be certain that your employer wouldn’t be loyal to you if the roles were reversed - you know this definitively, because they haven’t treated you well to date. Follow your gut, only you know what to do. But from just the text you provided, it sounds like it’s time to move on. As others have said be as professional as you can on the way out. 
 

and I probably wouldn’t take another counteroffer to stay, if you get one. I think you can do that move about once per employer per decade before you put a target on your head. You used that bullet already.

If you get your dream role, take it without hesitation. Thank your managers at your current firm for being great colleagues and being accommodating with your salary, and also make sure you say your decision is driven by a desire to pursue a different career track (just one of those nice things to say) and nothing your current firm has done.

And yeah, as someone said, they underpaid you for five years until you held a gun to their head so it's not like they're super benevolent people who you need to feel about about letting down.

It's one of the few times we get to use a cliche TV/Movie line: "it's not personal, it's just business" :)

If you believe the stat that 80% of people who accept counteroffers leave within 6 months of accepting said offer, they’re probably already trying to replace you. 

No one will ever pay you what you are worth. Be loyal to the business that pays the most for loyalty.

That promo role is prolly underpaid vs market.

Thanks everybody for their input. I have to admit it has put me at ease. I dont think it will be easy but I’ll keep you posted! 

I understand how you feel but keep emotion out of it. I recently changed career, and had some thoughts of how my current small boutique sized company (of which the owner is one of my best friends), would react. Drop those thoughts, and focus on whats best for YOU. They also underpaid you for 5 years, and they’re likely a huge company. The reality is nobody really cares about you like you’d hope/think.

Best of luck with the decision for YOUR career