An Investment Personal Pension (SIPP) is an investment vehicle that, by its nature, requires a long-term approach. As someone who believes in long-term investing, this suits me very well.

Here are three stocks that I think are outstanding and that, at the right price, I’d happily own in my SIPP.

Diageo

Beverage producer Diageo (LSE:DGE) is a stock I have been eyeing for some time. However, what I considered to be a high share price discouraged me from buying. However, last year saw a decline in prices. It is 15% lower than 12 months ago.

The price decline reflects investor concerns. The company’s delicate business performance in Latin America could be a sign of changes to come elsewhere, as needy economic performance and falling alcohol consumption among younger consumers threaten to reduce demand for top-shelf alcohol.

Despite this, Diageo has expanded into tender drinks in recent years. Meanwhile, the portfolio of premium beer and spirits brands continues to deliver profits year after year.

As a result, the company has an exceptional track record of increasing dividends per share every year for over three decades. This means that Diageo is one of FTSE100a few dividend aristocrats.

Spirax

Another one of these serial dividend harvesters is Spirax (LSE: SPX). Diageo may not be a household name (unlike many of its drinks) – but that’s even more true with Spirax.

The lack of widespread brand awareness is not surprising when selling industrial products such as steam engineering components to business customers. While it may not be glamorous, Spirax is a solid example of a successful business.

She identified a huge, resilient market. Its products are crucial to the polished operation of a wide range of industrial machinery, meaning customers are willing to pay a premium for quality even in a delicate economy. This has helped the company escalate its dividend every year for much longer than Diageo.

While Spirax has a track record of excellent business and exceptional dividend performance, this is also reflected in the share price.

Trading at 26 times earnings, Spirax is too high-priced for me to add to my SIPP at the moment. It faces risks, including delicate demand in China, which has already hurt profits. While revenues increased last year, after-tax profits fell by 18%.

Scottish mortgage loan

A Scottish mortgage investment fund (LSE: SMT) may not have increased its annual dividend per share with the same zeal as Spirax, but its record is still exceptional. The fund last cut its dividend in the wake of the 1929 stock market crash.

But that doesn’t mean it’s stuck in the past. Not at all. The investment fund has built a portfolio of growth stocks from countries around the world. Over the last five years, the share price is up 78% (even after falling 44% from its 2021 high).

Investing in companies with unproven models is risky. Scottish Mortgage, for example, owns a stake in battery manufacturer Northvolt, and the company currently faces significant challenges, including low-cost foreign competition.

However, over the long term, Scottish Mortgage’s approach has proven it can generate significant returns. I think this is a stock that investors should consider buying as a SIPP.