GET is limeted by the lenth of URLs alowed by the client and server, which ever is smaller.
POST is not limeted on any configuration I have seen.
A problem will be transfer and processing times. If each line is 16 characters on average then you will be sending 123KB (more when characters that have to be % encoded are used) Depending on the client connection that could take 30 seconds to a minute on a modem. After the server gets the data I assume it will have to 7000 update/insert SQL statments, that could take a decent lenght of time.
This could easily add up to a few minutes of time, not a lot from the programers perspective but it's a long time to sit and wait from a users perspective.
Comment on Re: Uploading Excel data into MySQL via a browser
While I encourage you to follow the advice of those advocating a file upload rather than a form field paste, you might be interested to know that (at least in IE5) you can change the enctype attribute for a form to 'text/plain' and it will send the server un-escaped text from your form rather than the normal 'x-form/urlencoded' (something like that) encoding type.